Traditionally, shock absorbers that damp shock in stopping a moving object by using fluid resistance of viscous fluid are fairly common, as disclosed in, for example, Patent Literatures 1 and 2.
A shock absorber of this type typically has a configuration in which oily liquid, such as mineral oil, is charged in a piston chamber, the piston for braking is housed in a state where a flow gap for the oily liquid is maintained, and a rod connected to the piston is extended to the outside of the cylinder housing. When the moving object collides with a leading end of the rod and pushes the piston, the oily liquid charged in the piston chamber moves in a direction opposite the sliding direction of the piston, kinetic energy of the moving object is absorbed by means of the flow resistance of the oily liquid flowing through the flow gap during that movement.
Typically, the above-described shock absorber has a configuration in which, when the moving object collides with the leading end of the rod protruding from the rod cover in a leading end portion of the cylinder housing and the rod retracts, the rod moves until the moving object comes into contact with the leading end surface of the rod cover and its stopping position is determined.
The rod cover is typically made of a metal, such as stainless steel. Every time the piston retracts due to collision with the moving object and the moving object collides with the rod cover, minute metal dust particles are typically produced by friction or the like caused by movement of displacement between the moving object and the rod cover, and before that, in addition, dust particles are also generated when the moving object collides with the leading end of the rod in most cases. Moreover, wear particles are also generated between the rod and a rod gasket or bearing member slidably supporting the rod in the cylinder housing. If metal powder adheres to a device under facility environment that deal with semiconductor devices or the like, the characteristics of the device may be affected. Accordingly, it is inappropriate to use the traditional shock absorber as it is in environments that dislike metal dust particles, such as the environments in the semiconductor manufacture field.
Examples of measures to address the above-described problems are described below. One example measure is that the shock absorber uses a configuration that reduces generation of dust particles when the moving object collides with the rod or rod cover as much as possible and that generates no wear particles between the rod and the rod gasket or bearing member in the cylinder housing. Another example measure is that the above-described dust-generating portion is covered to suppress flying dust particles, the dust particles in the dust-generating portion are sucked by force, and additionally, the moving object and the dust-generating portion where dust is generated from collision with the moving object in the shock absorber are moved to a location where the influence of the dust generation on the entire equipment is low. The former measure is expected to be achieved at reduced cost. With the latter measure, the equipment may lead to increased cost. Thus, the former measure is needed to reduce the generation of dust particles.
Furthermore, in the above-described shock absorber, if dust particles or the like generated in the above-described way are on the rod when the moving object collides with the rod protruding out from the cylinder housing, they enter the cylinder housing and cause wearing out of the internal structure or the like. Thus, it is necessary to arrange a dust-resistant wiper or the like around the rod to suppress the entry of foreign substances. Because the rod is supported on the bearing in the cylinder housing with an oil film for lubrication disposed therebetween, there is also a necessity to prevent the oil film for lubrication from leaking out over the bearing, in addition to the necessity of suppressing the entry of foreign substances into the cylinder housing. If the leakage of the oil film for lubrication proceeds, even the oily liquid charged in the cylinder housing and absorbing kinetic energy of the moving object by its flow resistance leaks out, and the performance as the shock absorber is finally lost.